Traditionally, surface contaminants such as oil, grease and other organic and inorganic compounds are removed from substrate surfaces such as semiconductors, metals, ceramics, magnetic materials, plastics and optical device surfaces, by wet cleaning processes. These wet cleaning processes conventionally comprise placing the object to be cleaned into an organic solvent such as carbon fluorochloride and trichloroethylene and vibrating it by subjecting it to ultrasonic waves. The chemical action of the solvent, in combination with the physical action of the ultrasonic waves, achieves the cleaning of the substrate surface.
This wet cleaning method effectively removes most organic contaminants, however, there are several undesirable aspects of this cleaning process which the present invention avoids. Organic solvents such as trichloroethylene and carbon fluorochloride are hazardous to human health and their use entails a health risk to workers handling them. Particularly, when applying ultrasonic waves to an organic solvent bath, there is a heightened health risk resulting from the vaporization of the solvents. Furthermore, the exposure of workers to the noise generated by ultrasonic wave machines presents an independent health hazard. One that may have long term consequences. Additionally, the use of these organic solvents also pose a risk to the environment. Carbon Fluorochloride has been implicated in the depletion of the Earth's ozone layer and leakage of these solvents into the environment may cause serious pollution and damage. Disposal of waste solvents presents yet another difficulty encountered when using this organic solvent cleaning method.
Apart from the obvious health and environmental concerns involved with these wet-cleaning processes, there are difficulties inherent in their application. The process is inefficient and costly, requiring several steps to exchange the cleaning solvents and exchange of substrates. This makes the process not feasible for some applications.
More importantly, these ultrasonic cleaning processes have difficulties cleaning surfaces of substrates which react chemically with the cleaning solvents. Where the reaction of the substrate to the solvent is strong, this method of cleaning may be unacceptable.
Finally, these cleaning processes are limited in that they cannot clean the surface of articles which are larger than the ultrasonic cleaning basin.
In an effort to avoid the inherent disadvantages of ultrasonic solvent cleaning methods, other cleaning methods utilizing lasers have been developed. Laser cleaning by annealing or melting require high energy lasing as well as costly operating conditions. These cleaning methods often require that the work be done within a vacuum chamber in order to remove the contaminants released from the surface. Utilizing a vacuum chamber is costly and time consuming. It may also restrict the size of the work-piece to be cleaned.
Additionally, cleaning by annealing and by melting reconfigures the physical structure of the surface of the structure to be cleaned. This is undesirable when the integrity of the surface to be cleaned must be maintained.
Other laser cleaning methods employ a method of saturating the surface being cleaned with an inert gas. Such operations require methods of flowing a gas over the work surface which in turn requires a containment vessel for the work-piece and a means to circulate the gas over the work surface. This presents the obvious disadvantage of cost and time consumption.